The present invention relates generally to a system for optically transferring information via luminous energy among two or more stations. More particularly, this invention pertains to a system for transferring information via light signals from at least one station to another station when one of the stations is generally capable of movement with respect to the other.
As is appreciated by those skilled in the art, it is often desirable to transfer information or control signals by light energy rather than by electrical energy, especially when the constraints of the operating environment preclude using conventional electrical information transfer systems. For example, in some environments it is necessary to transfer information or control signals between two electrical circuits when one of the electrical circuits is operating with respect to a ground reference level which is different from that of the other electrical circuit. Optical information transfer systems are particularly suitable for this application because they have the inherent property of electrically isolating the reference voltage level of one electrical circuit from that of the other. The light weight of optical information transfer systems and their immunity to electrical interference are further properties which make these systems especially useful in weapon systems and aircraft control systems where high reliability and survivability are critical. Optical information transfer systems are also ideal for use in explosive and inflammable environments in order to avoid the hazards associated with conventional electrical circuits.
One of the more perplexing problems faced by designers, manufacturers, and users of light information transfer systems, has, for a number of years, been, and continues today to be, the need to transmit information and control signals between one station that is moving with respect to a second station, or between two or more stations moving at different speeds relative to each other. In this connection, many efforts have been made, and are continuing to be made, to solve this problem. Initially, information was transferred by electrical signals and such efforts were primarily directed towards providing various forms of electrical slip rings for making electrical connections between a stationary source of electrical signals and a rotating receptor of the electrical signals. Typically, metal rings were mounted on the rotating portion of the apparatus and the stationary brushes that were connected to the source of electrical signals wore against the metal rings and conducted current into or out of the rotating member. This system was inherently susceptible to electrical and mechanical noise originating from the poor connection between the brushes and slip rings. The system was also limited in its frequency response due to the variations in the characteristic impedence of the slip rings.
With respect to transferring information optically, other efforts directed towards solving this problem have included use of a derotating prism which is arranged to rotate at one-half the speed of relative rotation between the rotating and stationary portions of an apparatus. A typical example of this approach is suggested in Iverson, U.S. Pat. No. 4,027,945, in FIG. 4. The derotating prism shown therein is a direct vision prism which will invert an image in one position, but when turned 90.degree. will reinvert the image. This property causes an image to rotate at twice the rate that the prism is rotated. By rotating the prism at half the speed of the rotating object, its image will appear to be stationary after passing through the prism.
In addition to the derotating prism suggestion contained in the aforesaid Iverson Patent, Iverson discloses other variations for transferring light signals from a rotating body to a non-rotating body by using multiple channels, waveguides, concentric annular mirrors and optical slip rings. The optical slip ring embodiment contains bundles of optical fibers which are placed end to end coaxially with the axis of rotation. Light introduced into one bundle travels to the opposite end where it couples across a small gap into the second bundle. Multichannel bundles are used by forming channels at the coupled ends into concentric circles separated by an opaque material.
There has been a wealth of work expended in the area of illuminating panels and instrument dial plates by injecting light into one or more of the surfaces of the panel or dial plate. For example, in Dros, U.S. Pat. No. 2,770,712, a dial plate is illuminated by projecting light rays axially onto a rod having a cone shaped indentation in the end of the rod that is attached to the dial plate so that the incident light rays are projected into the plate in radial directions. See also, Hardesty, U.S. Pat. No. 2,831,453 which discloses an illuminated panel wherein light which travels in a plane parallel to the panel is intensified at desired locations in the panel by reflecting from angular surfaces located below the areas desired to be highlighted. Baker, U.S. Pat. No. 2,900,949, discloses an arrangement for illuminating instrument dials by providing the dial with elliptical corners and placing a light bulb at the focal point of each ellipse such that light from the bulb is evenly reflected from the corners of the instrument dial to all areas in the plane. The light rays concentrated at the center of the panel are reflected from a truncated conical surface to a pointer located on either side of the panel. Huther, U.S. Pat. No. 3,609,960, discloses a time piece dial wherein cones are placed below the hour marks so that light emitted from a bulb embedded in the time piece dial is reflected from the cones and highlights the hour marks.
The concept of using lenses, mirrors and reflective surfaces to collimate or modify the direction of light energy is described in the art, for example, by Stechemesser et al, U.S. Pat. No. 3,240,113, which discloses an arrangement of mirrors and lenses which are used to project panoramic photography at a horizontal angle of view of up to 360.degree.. Other representative patents showing mirror and lens configurations include, for example: Freiberg, U.S. Pat. No. 4,025,172 and Rambauske, U.S. Pat. No. 3,802,767.
Other representative patents of miscellaneous interest include, for example, Bartok et al, U.S. Pat. No. 3,800,058, which discloses an electro-optical organ employing a rotating disk having numerous concentric tracks of varying opacity and a light source for diverting light through all of the tracks to establish a time varying light beam representative of musical tones. The concept of using opposed reflecting surfaces which transmit incident light by multiple reflections for the purpose of increasing the efficiency of a solar panel is disclosed in Kapany, U.S. Pat. No. 4,078,548. A meter for measuring electrical quantities which uses a bi-concave lens at the center of a moving part is disclosed by Sklyaruk et al, U.S. Pat. No. 3,596,178. A camera having an apparatus in the region of its view finder for indicating the adjustment of the camera is disclosed by Papke, U.S. Pat. No. 3,675,552. The apparatus is formed in a frustoconical configuration having a large end forming a light receiving surface and a small end forming a light discharging surface with the small end being annularly shaped with an indentation defining the inner edge of a light discharging surface. The surface of the indentation can be coated in order to improve the efficiency of the device. In the Ferris Patent, U.S. Pat. No. 3,221,593, a cone is used to permit visual inspection of the inside of boiler tubes or other industrial piping.
Consequently, insofar as is presently known, while the prior art is replete with numerous proposed processes for illuminating dial plates and proposed techniques using complex fiber optic cables and or mirrors and lenses requiring relatively large space and being therefore limiting in application for transmitting light signals, prior to the advent of the present invention there has been no known effective and reliable method or apparatus that is simple in construction and capable of permitting information to be transferred by light signals from a first station to another station that is moving with respect to the first station.